Abstract
Abstract
Strips of muscularis propria were so cut that contractions would represent actions of smooth muscle of longitudinal and circular layers of esophageal body and circular layer of esophagogastric sphincter, oblique layer of gastric fundus and circular layer of pylorus and ileocecal junction. Isometric tone, a force maintained in the absence of stimulation, was present only in fundus and sphincter strips. Strips from esophageal body contracted in response to electrical field stimulation of intramural nerves: in longitudinal muscle these responses were atropine sensitive; in circular muscle they were not. Oxygen dependence was tested by equilibrating bath solutions with gas mixtures in which nitrogen incrementally replaced oxygen, and by exposing strips to metabolic inhibitors. Isometric tone in all sphincter and fundus muscles declined as oxygen was replaced with nitrogen. It was abolished by metabolic inhibitors. Neurogenic contractions of both layers of esophageal body muscle and the contractions induced by carbachol, histamine, and substance P in sphincter strips were not oxygen dependent. Thus, isometric tone in gastrointestinal muscle differs from other kinds of contractions in its requirement for oxygen.
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